Problem: $ { {5} \times \left[\begin{array}{r}{1} \\ {4} \\ {3}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{5}\times{1} \\ {5}\times{4} \\ {5}\times{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{5} \\ {20} \\ {15}\end{array}\right]}$